Siren



0. I. H. EKMAN SIREN Sept. 26, 1939.

2 sheets-sheet 1 Filed Nov. 3, 1936 Sept. 26, 1939. o, EKMAN 2,174,125

SIREN Filed Nov. 5, 1936 2 she'ets sheet 2 -25 as circular plates.

Patented Sept. 26, 1939 UNITED STATES PATENT OFFICE Application November3, 1936, Serial No. 109,012 In Sweden October 29, 1935 6 Claims.

In sirens of the type in which a diaphragm is used as the soundproducing member, for instance, selective horns, it is necessary undercertain conditions, in order to promote the acoustic effect, to increasethe operative surface of the diaphragm. This increase, however, cannotbe extended unlimitedly, for the reason, amongst others, that, as thesurface of the diaphragm is increased it may become too large to respondto the frequency, the driving power tends to impart to it. In order toovercome this difficulty, to a certain extent at least, the drivingpower may be distributed over the diaphragm, for instance, by the use ofcompressed air or the like 5 for effecting the vibrations of thediaphragm instead of, as in the usual magnetic signalling horns,allowing the driving power to act on a small area of the diaphragm only.This limitation of the size of diaphragm is due, substantially, to theincreased inertia of the larger diaphragm and the increased effectiveresistance of the masses of air to be caused to vibrate by thevibrations of the diaphragm.

As a rule, the diaphragms of sirens are formed Such diaphragms,especially those of larger area, present, in addition, the difficulty,that their principal tone is not fully clear, as a superposing mayeasily occur as a result of natural vibrations of different frequencies.Great difficulties are, therefore, experienced in attempting to obtain adiaphragm of this type which presents a clear tone and is capable ofeasily getting into resonance with the impulse producing source ofpower.

For the generation of tones of a higher frequency by the aid of a soundemitting horn of usual design, it is impossible to use too large adiaphragm, as sound waves emitted from the peripheral portions of thediaphragm, will interfere disadvantageously with waves of a later phaseemitted from the central portion of the diaphragm.

The present invention has for its object to provide a diaphragm, bywhich the difiiculties above stated will be overcome. The invention ischaracterized, chiefly, by a circular set of diaphragms and means foralternately loading and relieving those diaphragms, either in groups orall at the same time, in order to cause them to vibrate.

In the accompanying drawings various embodiments of the invention areillustrated. Fig. 1 is an axial section taken on the broken line l-| ofFig. 2 of an embodiment having radially arranged diaphragms. Fig. 2 is across section of said embodiment, taken on the line 2--2 of Fig. I. Fig.3 is a development of a vertical section as taken centrally through thevalve disc and the diaphragms of the embodiment of Fig. 1. Fig. 4 showspart of an axial section of the embodiment 5 of Fig. 1, as taken betweena pair of diaphragms, with the horn removed. Fig. 5 is a side elevation,and Fig. 6 is a plan view of a diaphragm clamping device. Fig. 7 is aplan view of part of a diaphragm and valve mechanism according to a 10modified embodiment of the invention. Fig. 8

is a developed cross section through the centre of the annular portionshown in Fig. 7. Fig. 9

is a vertical section of another modification of the diaphragm and valvemechanism. Fig. 10 15 is an axial section of a horn of a modifiedembodiment.

In the embodiment shown in Figs. 1 and 2, the numeral I indicates areceptacle, adapted to receive a compressed fluid, as compressed air, 2which may be either supplied thereto from some external source orproduced within the receptacle by means of a compressor disposedtherein.

At its top the receptacle carries a ring 2 which presents a cylindricalinner surface 3 at its upper 25 mouth. Said surface is adapted to act asthe slide face for a rotary valve in the shape of a disc 4 keyed to acontrol driving shaft 5. The valve disc 4 presents an undivided, centralportion by which it is attached to said shaft and an 30 annularperipheral portion having a set of radially extending ports 6 leadingthrough the disc from its lower to its upper surface, as shown to theright of Fig. 1, and alternately therewith, a set of radial grooves 1formed in the up- .35 per surface of the disc which lead to theperiphery of the disc, right in front of the slide face 3, as shown tothe left of Fig. 1. Formed in the ring 2 is a series of ports 8 adaptedto communicate with the grooves I of the valve disc when 40 thesegrooves pass right below the diaphragms, that is to say, the ports aresituated each outside its respective diaphragm. The diaphragms 9 arelocated above the annular portion of the valve 'dis'c. They extendradially and their form and 45 position correspond to those of theopenings or grooves of the valve disc. The spacing of the diaphragms isequal to that of the opening 6 or grooves l of the valve disc.

The distance between each two adjacent open- 50 ings 6 or grooves l ofthe valve disc at the inner circumference of the annular disc portion isequal to the width of a diaphragm. The distance between each twoadjacent diaphragms 9 of this embodiment will, as a result, be threetimes the 55 distance between each two adjacent openings or grooves.

The diaphragms 9 are made from elastic sheet metal of great strength,preferably by cutting off suitable lengths from a band of special steel.Each diaphragm extends between the ring 2 and a centra1 clamping discl0, situated above the central portion of the valve disc 4 and carrying,if desired, a bearing H for the shaft 5. As shown, each diaphragm isrigidly secured to the inner clamping disc and is further attached to aflange I2 of the ring 2 by means of a pair of cross pieces l3, H, seeFigs. 5 and 6, between which the upwardly bent outer end of thediaphragm is clamped by means of a pair of screws l5, the cross pieceswith the clamped end of the diaphragm being then attached to the-flangeI2 by means of a central screw I6 while exerting a pressure that can bevaried by the edge of a nut I1. Inthis attachment the diaphragm bears'onedges i8, #9 of the members 18 and 2, respectively, in order todetermine the operative length of the diaphragm. By this means, eachdiaphragm may be adjusted to produce its individual, practically cleartone in the same way as in the case of an instrumental chord, thenatural frequency of the diaphragm being easily adjustable. After all ofthe diaphragms have been adjusted so as to produce the same tone, thediaphragms as a whole will represent a unitary diaphragm having a cleartone, all portions of which will always simultaneously vibrate inresonance with the vibrating power acting on the individual diaphragms.

The ring 2 and the central clamping member it for the diaphragms areconnected together by means of beams or spokes 20 extending between saidring and member alternately with the individual diaphragms. It is thusseen that the said inner portion I0 is carried by the ring 2 by means ofsaid beams or spokes, at the same time that the latter divide the spaceabove the diaphragms into separate sound passages extending from thevarious diaphragms. The beams or spokes 20 are so formed as to conformat their under side with the smallest clearance possible with relationto the upper side of the annular portion of the valve disc 4, said upperside being shaped in conformity with a downwardly curved surfacecorresponding to the maximal downward bending of the diaphragms, seeFig. 4. Furthermore, the beams 20 fit with the smallest clearancepossible to the lateral edges of the diaphragms 9 in order to preventleakage of air at the sides of the diaphragms. Placed over the centralclamping member ID and the beams 25 is a cover comprising, in theembodiment shown, an inner wall 2! covering the central clamping memberl0, and an outer wall 22, supported by the ring 2, so that there will bean annular chamber between said two walls into which the beams 20project, causing said chamber to branch at its lower end into theseparate sound passages leading from the diaphragms. The inner wall 2|may be held in place by being forced down between the cylindricallyturned inner ends of the beams 20. At its top the outer wall 22 isconnected to a central horn which may be rotatable for the spreading ofthe sound in various directions. The beams 20 are preferablywedge-shaped with the edge directed upwardly, as shown in Fig. 3, and,furthermore, they grow thicker and higher towards their outer periphery,in order that the individual sound passages may present substantiallythe same cross section area at the outer periphery as they do at theinner periphery. The operation is as follows:

During the rotation of the valve disc, the vertically through-extendingopenings 6, that is to say, the loading openings, and the grooves I,that is to say the relief channels, will alternately pass below thediaphragms. When the openings 6 pass below the diaphragms, compressedair contained in the receptacle l is allowed to act on the under side ofthe diaphragms, forcing them upwardly so as to cause them to produce apressure wave in the horn, resulting in the emission of a tone. When,thereupon, the grooves 1 pass below the diaphragms, the compressed aircontained between the upwardly bent diaphragms and the valve disc willbe allowed to escape through the ports 8 of the ring 2, allowing thediaphragms to swing down again by their elasticity. As will appear fromFigs. 2 and 3, a groove 1 will not enter the space below a diaphragmbefore the preceding opening 6 has completely left the range of thisdiaphragm. In other words, at any time only the openings 6 or thegrooves I are in position below the diaphragms.

The frequency depends on the number of revolutions of the valve disc aswell as on the number of diaphragms. An increased frequency may thus beobtained by increasing the number of revolutions of the valve disc or byincreasing the number of diaphragms, or by these two measurements inconjunction.

In order to be able to increase the number of diaphragms I may, forinstance, as shown in Figs. 7 and 8, make the openings 6 and the grooves"I of the valve disc 4 of less width than the diaphragm, as, forinstance, equal to a third of the width of the diaphragm, as shown insaid figures. In this case it is thus possible to reduce the spacing ofthe diaphragms to half that of the above described embodiment. As willappear from Fig. 8, in this embodiment a loading opening 6 and a reliefpassage 1 will simultaneously pass below different portions of one andthe same diaphragm, so that said opening will enter below the diaphragmwhen said passage leaves the diaphragm, and vice versa. As a result,there will be a successively progressing increase of pressure and alikewise successive relieving of the pressure on the diaphragms duringeach cycle of operation. In this embodiment the pressure will at anymoment be applied to part of each diaphragm only, but as there is acertain clearance between the valve disc and the diaphragm, that cannotbe avoided, practically the whole diaphragm will be under pressureduring the passage of a loading opening therebelow.

Another embodiment is illustrated in Fig. 9, in which openings orpassages and diaphragms are .of the same width, though the diaphragm isshielded off at both of its sides by means of projections 30 of thebeams 25!, thereby only exposing the central portion of the diaphragm tothe action of the pressure.

In order that the horn may act in the most eflicient way care should betaken that the vi.bra tions are led out symmetrically from various radiiof the diaphragms. To this end the two walls 2| and 22 of the baseportion of the horn may be symmetrical, as shown in Fig. 10.

In the constructions above described, the pressure prevailing in thereceptacle I is also always existing in the openings and is therebyallowed to immediately act upon the diaphragms as soon as they areuncovered by said openings, without the necessity of filling any largerspace prior to each operation of a diaphragm. Due to the positioning ofthe valve disc in close proximity of the diaphragms, the loading and therelief of the dia phragms will take place at a minimum loss of time. Bythe use of separate openings for the loading and the relief, adifference of the direction of flow in the individual openings neednever be taken into consideration, whereby the occurrence of undesiredflows will be avoided, and losses of energy and time reduced.

In the embodiments described, the diaphragms are disposed in asubstantially plane surface, in which they extend radially with respectto a centre representing the axis of rotation of the rotary valvecontrolling the admission and discharge of the driving fluid acting onthe diaphragms. Said embodiments are particularly well adapted forsirens of small and moderate sizes.

If instead of compressed air or another compressed fluid of normaltemperature there is used, for instance, hot combustion gases to actupon the diaphragms, the latter due to their heating will be subjectedto a certain extension which in case of the diaphragms being rigidlyclamped will reduce the stress thereof to such an extent as to result inan undesired tone. To avoid this drawback, the diaphragms may be heldstretched by means of springs, preferably long coiled springs of such aninitial stress, that the extension the spring may undergo owing to theextension of the diaphragm, will produce a neglectable change of thestress only.

Instead of compressed air or another pressure fluid to effect theoperation of the diaphragm, I may use some other power, aselectromagnetic force.

What I claim is:

1. A siren having, in combination, a receptacle to receive a fluid underpressure, said receptacle having an end wall and an annular set ofopenings therein, diaphragms in said openings, a rotary disc in thereceptacle in close proximity to the diaphragms, a set of axiallythrough-extending openings in said disc and a set of grooves in thesurface of the disc facing the diaphragms, said grooves being arrangedalternately with said openings and ending at the outer periphery of thedisc.

2. A siren having, in combination, a receptacle to receive a fluid underpressure, said receptacle having an end wall comprising a centralportion, an annular peripheral portion and radial connecting memberstherebetween, said connecting members forming apertures betweenthemselves, diaphragms inserted in said apertures, means to adjust themechanical stress on the diaphragms, edges on said portions to beengaged by the diaphragms to fix the operative length thereof, a rotarydisc in said receptacle in close proximity to the diaphragms toalternately subject the diaphragms to the action of the fluid in thereceptacle and relieve them therefrom,

3. A siren having, in combination, a receptacle to receive a fluid underpressure, said receptacle having an end wall formed with an annular setof openings, diaphragms in said openings, a rotary valve disc providedin said receptacle in close proximity to the diaphragms, said valve dischaving passages to alternately expose the diaphragms to the action ofthe compressed fluid and relieve them therefrom, and a horn having anannular base chamber mounted on said end wall of the receptacle outsidethe diaphragms,

said end wall comprising an undivided central portion, an annularperipheral portion concentric to said central portion and spaced radialconnecting members between said portions, said connecting membersprojecting into the annular base chamber of the horn so as to formpartitions between sound passages leading from the various diaphragms tothe horn.

4. A siren having, in combination, a receptacle to receive a fluid underpressure, said receptacle having an end wall formed with an annular setof openings, diaphragms in said openings, a rotary valve disc providedin said receptacle in close proximity to the diaphragms, said valve dischaving passages to alternately expose the diaphragms to the action ofthe compressed fluid and relieve them therefrom, and a horn having anannular base chamber mounted on said end wall of the receptacle outsidethe diaphragms, said end wall comprising a central portion, a concentricperipheral portion, and a set of spaced radial connecting membersbetween said portions, said connecting members projecting into theannular base chamber of the horn and tapering upwardly and inwardly soas to present a uniform transition from the sound passages to the horn.

5. A siren having, in combination, a receptacle to receive a fluid underpressure, said receptacle having an end wall formed with an annular setof openings, diaphragms in said openings, a rotary valve disc providedin said receptacle in close proximity to the diaphragms, said valvehaving passages to alternately expose the diaphragms to the action ofthe compressed fluid and relieve them therefrom, and a horn having anannular base chamber mounted on said end wall of the receptacle outsidethe diaphragms, said end wall comprising a central portion, a concentricperipheral portion, and a set of spaced radial connecting membersbetween said portions, said connecting members projecting into theannular base chamber of the horn and tapering upwardly and inwardly soas to present a uniform transition from the sound passages to the horn,the surface of valve facing the diaphragms being shaped in conformitywith the maximum deflection of the diaphragms and the surface of saidpartitions facing the valve being formed in conformity with said surfaceof the valve in order to secure maximum sealing effect between thepartitions and the valve.

6. A siren having, in combination, a receptacle to receive a fluid underpressure, said receptacle having an end wall comprising a disc-shapedcentral portion, an annular peripheral portion concentric therewith, anda set of spaced connecting members between said portions, diaphragmsinserted in the spaces between said connecting members, a rotary valvedisc arranged in the receptacle in close proximity to said end wall,said diaphragms comprising radial tapes extending from said centralportion to said peripheral portion, separate means including clampingdevices to connect the individual diaphragms to one of said portions soas to permit adjustment of the diaphragms for the same tone, theclamping devices for the outer ends of the diaphragms comprising each apair of clamping members for the end of the diaphragm and a central boltto connect said clamping members to the annular peripheral portion ofsaid end wall.

OLOF INGEMAR HARALD EKMAN.

